Java ArrayList中最常见的n个单词 [英] Most frequent n - words in java ArrayList

问题描述

我需要在ArrayList中找到最常用的单词(n个单词，所以如果n = 5，则最常用的5个单词).

I need to find the most frequent words (n words, so if n = 5, the most frequent 5 words) in an ArrayList.

private ArrayList<String> wordList = new ArrayList<String>();


public ArrayList<String> mostOften(int k)
{
    ArrayList<String> lista = new ArrayList<String>();
    Set<String> unique = new HashSet<String>(wordList);
    for (String key : unique) 
        System.out.println(key + ": " + Collections.frequency(wordList, key));

    return lista;
}

该函数需要返回最频繁单词的列表，并按频率排序.如果2个单词的频率相同，则需要按字母顺序对其进行排序.我已经发布了我尝试过的内容，但这只能找到频率，其余的我不知道该怎么做.有帮助吗?

The function needs to return a list of the most frequent words, sorted by frequency. If 2 words have the same frequency, I need to sort them alphabetaclly. I have posted what I tried, but this only finds the frequency and I do not know how to do the rest. Any help?

推荐答案

您可以编写一个用列表初始化的Comparator类.然后，您可以使用列表和Comparator调用Collections.sort(). 代码可能看起来像这样:

You could write a Comparator class which is initialized with the list. Then you could invoke Collections.sort() with the list and the Comparator. The code might look like this:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class FrequencyComparator implements Comparator<String>{

    List<String> list;

    @Override
    public int compare(String o1, String o2) {
        if (Collections.frequency(list, o1) > Collections.frequency(list, o2)){
            return -1;
        }else if (Collections.frequency(list, o1) < Collections.frequency(list, o2)){
            return 1;
        }else{
            return o1.compareTo(o2);
        }
    }

    public FrequencyComparator(List<String> list){
        this.list = list;
    }

    public static void main(String[] args)
    {
        List<String> list = new ArrayList<String>();
        list.add("Hello");
        list.add("You");
        list.add("Hello");
        list.add("You");
        list.add("Apple");
        list.add("Apple");
        list.add("Hello");
        Set<String> unique = new HashSet<>(list);
        List<String> uniqueList = new ArrayList<>(unique);
        Collections.sort(uniqueList, new FrequencyComparator(list));
        System.out.println(uniqueList);
        //Take the most frequent 2 objects
        System.out.println(uniqueList.subList(uniqueList.size() - 2, uniqueList.size());
    }

}

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